The Oxo Process or Oxo-Synthesis is a well-established reaction of commercial import. (See: KirkOthmer, "Encyclopedia of Chemical Technology", 2nd Edition, Vol. 14, 373-390 [1967]; The Merck Index, 8th Ed., page 1197 [1968]; U.S. Pat. No. 3,462,500 of Tummes et al; and citations therein.). It is used in the industrial manufacture of aldehydes and alcohols from olefins, carbon monoxide and hydrogen. Unfortunately, undesirable formic acid esters of the corresponding alcohols are concurrently obtained to a considerable extent as unwanted by-products.
The formation of the esters reduces the yield of the more valuable aldehydes and alcohols. Furthermore, it is difficult to separate the esters by distillation from the reaction product. Finding a way to convert the formic acid esters into corresponding alcohols or aldehydes (if possible, without any large expenditure and without loss) is thus a most desirous goal.
These esters are conventionally saponified with acids or alkalis; mineral acids or Lewis acids (DAS [German Published Applications] 1,108,195 and 1,148,221) or alkaline-reacting substances (DAS 1,085,513) are used. However, such saponification leads to corrosion problems, particularly when acids are employed. Moreover, larger losses in yield are incurred when aldehydes are still present; the latter are difficult to separate from the alcohol mixture.
Saponification with mild alkali at elevated temperature, whereby decomposition to alcohol and gaseous products (CO.sub.2,H.sub.2,CO) takes place (DAS 1,258,855), is also undesirable because of the high pressures and temperatures required, especially since the alkali salt and the water of condensation must be constantly replenished during continuous operation.
In contrast thereto, cleaving hydrogenation of the formic acid esters is desirable, since a hydrogenation step is necessary in the production of alcohols, particularly according to the Oxo Process, in order to remove the hydrogenatable compounds, such as aldehydes and compounds with double bonds. For this purpose, conventional nickel catalysts are available. However, DAS 1,258,855, col. 4, advises against such a mode of operation, particularly because the high nickel consumption, resulting from unavoidable catalyst poisoning caused by the carbon monoxide, makes this process uneconomical.
H. Adkins reported ("Organic Reactions", 8, 1-27 [1954] on the hydrogenation of esters to alcohols with only copper chromium catalysts, zinc chromium catalysts or Raney nickel catalysts. The more advantageous use of the catalysts of the subject invention in conjunction with formic acid esters, which was not reported by Adkins, could not be derived from the cited article.